It is widely acknowledged that the human visual system is much more sensitive to variations in brightness than color. Chroma downsampling is based on this principle. Chroma downsampling involves encoding images by implementing lower resolution for Chroma information than for Luma information and is widely adopted in the field of digital image compression. Many digital SLR cameras use 2×1 chroma subsampling, and some point and shoot digital cameras use 2×2 chroma subsampling. Some graphics programs (such as Photoshop) sometimes use 2×2 (4:2:0) chroma subsampling.
In Towards Better Chroma Subsampling (published in SMPTE Motion Imaging Journal, 2008 5/6 May/June), Glenn Chan submits that chroma downsampling is not visually lossless in all situations and examines sources of chroma subsampling artifacts. Chen discloses a technique for extracting higher quality from existing chroma subsampled signals by minimizing out of gamut colors.